11. Light travels in a .......
12. Light selects the least time path to travel between two points.
This principle was stated by .......
13. Magnification m = Height of the image/ .......
14. The pH of neutral solution is ......
15. Our stomach produces ..... acid.

16. Bases turn ...... to different colours.
17. ...... tube is used to dry a gas.
18. Salts are electrically .......
19. ....... is used as a reagent in the preparation of chloroform.
20. Acids react with some metals to produce ........ gas.